The invention is concerned with analytical methods for determining surface and interface properties.
Surface and interfacial phenomena at the junction between dissimilar media have been of longstanding interest, e.g., in metallurgy, soil engineering and agronomy, energy conversion, medicine, and the electronics industry. Increasingly also, such phenomena are receiving attention in other fields including biological and environmental studies, for example.
For the selective probing of surface properties, the use of nonlinear optical processes such as second harmonic generation (SHG), sum frequency generation (SFG) and difference frequency generation (DFG) has been found to have advantages over other methods, e.g., as based on observing fluorescence. In particular, as compared with the latter, methods based on nonlinear optical processes do not require the introduction of an extraneous agent for light emission at the surface to be studied. Advantageously further, the SHG and SFG methods can be used to study buried interfaces such as liquid-liquid, liquid-solid and solidsolid interfaces, whereas other surface techniques can be used only for vacuum-solid interfaces. The SHG and SFG methods are highly surface specific, and they can be used to study surface dynamic processes with sub-picosecond time resolution as well as static processes.
In most cases, SHG and SFG experiments are performed on planar surfaces. This has restricted the range of systems studied.